In many electronic systems there is a need for a precision analog voltage reference that is independent of time, temperature, and process variations. For example, analog-to-digital converters typically require an analog voltage reference. In many voltage reference circuits, a first voltage source that has a positive temperature coefficient (voltage increases with temperature) is summed with a second voltage source that has a negative temperature coefficient and the two temperature dependencies cancel. For example, in one common design (called a bandgap reference, or sometimes a Browkaw bandgap reference) the base-to-emitter voltage of a bipolar-junction-transistor is used for a first voltage having a negative temperature coefficient, and the difference between two base-to-emitter voltages is used for a second voltage having a positive temperature coefficient, and the two voltages are scaled and summed. After adjustment, such a circuit can typically provide a voltage reference having about one percent voltage variation over a specified temperature range. However, some systems need a voltage reference having better than one percent accuracy over a specified temperature range. There is an ongoing need for a higher precision voltage reference.